"However, the web has the potential to increase the anxieties of people who have little or no medical training, especially when web search is employed as a diagnostic procedure," they say.

"Common, likely innocuous symptoms can escalate into the review of content on serious, rare conditions that are linked to the common symptoms," the researchers add.

For example, web surfers with a headache may determine they have a brain tumour or those with chest pain that they are suffering a heart attack.

"A brain tumour is a concerning possibility when a searcher experiences headache," the researchers say. "However, the probability of a brain tumour given a general complaint of headache is typically quite low."

"Such escalations from common symptoms to serious concerns may lead to unnecessary anxiety, investment of time, and expensive engagements with healthcare professionals," White and Horvitz say.

The researchers say search engine architects have a responsibility to work against cyberchondria by, among other things, improving the way search results are ranked.

"They must be cognisant of the potential problems caused by cyberchondria, and focused on serving medical search results that are reliable, complete, and timely as well as topically relevant," say White and Horvitz.

Not convinced

Australian researcher Dr Annie Lau of the Centre for Health Informatics at the University of New South Wales says the study is interesting but does not support the conclusion that people are suffering cyberchondria.

She says the study looked at web logs but not what people actually did.

Lau says those who begin searching about headaches may simply be going on to pages on brain tumours out of curiosity.

"Whether people are suffering from cyberchondria or simply wanting to get more information about a health topic, we can't tell at this stage," Lau says.

But, she says more research is needed to improve the way people use the web to inform and manage their health care.